Boll-Aero 1.8cc Diesel

[HopperParticipant @hopper]

Silver steel can be a bit brittle like that under shock loading. I learned that many years ago when I made a front axle for my BSA Bantam paddock bike out of a bit of silver steel from Dad's shed. It didn't last long before snapping — right on the end of the thread we cut for the axle nut. We used 4140 after that and had no problems. I think the UK equivalent is EN19A. It was some pretty severe duty being smashed over bumps and jumps on the dirt tracks with forks that bottomed out regularly due to total lack of damping!

 

Edited By Hopper on 16/08/2020 11:46:56

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Thank you everyone that has shown interest in this project. The one thing we all seen to agree on is that Silver Steel is not good for a component that is to have a thread and will be stressed in use

Keith

[dean clarke 2Participant @deanclarke2]

You will find that when you heated the silver steel to solder you hardened it but without the next step of tempering you left the shaft hard, and therefore brittle. The sudden shock of the backfire was enough to fracture the component and the running loads brought to completion the part failure. A simple mistake to make when not understanding the metallurgy of the materials one is working with (from my own experience (lol) its usually better to machine the crank from solid anyway.

very nice engine to by the way.

Regards

Dean

[JasonBModerator @jasonb]

I doubt it got hardened unless Keith quenched it but he says he allowed it to cool naturally which in my book is annealing.

[Harry WilhelmParticipant @harrywilhelm18718]

Nice looking job! The Boll Aero is a very clever design. The simplicity cannot be beat, yet a lot of customization is possible. Model engine news has pictures showing many different interpretations of this design. Mine is the one with the black anodizing. Yours is very similar to mine, but with your own personal touches.

I built an R/C carb for mine and on the test stand would idle at around 1900 rpm with a top end of around 7200. APC 9×6 propellor. I have some hand drawn plans for the carb if you are interested.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Harry,

I have sent you a PM.

Keith

[Grindstone CowboyParticipant @grindstonecowboy]

My copy of "The Vintage Motorcyclist's Workshop" by "Radco" advises never to use silver steel for spindles, or any parts of the suspension e.g. in girder forks.

Now we know why.

Rob

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